When the roof, not the bill, sets the system size
On a detached house the usual sizing question is how much of your consumption to cover. On a rowhome it is often simpler and harsher: how many panels fit properly on the area you own. Single-attached units are 51.8 percent of the housing stock here, so that is the common case.
When area is the binding constraint, the priority shifts from maximising size to maximising quality. Every panel has to sit on a plane that produces well, because there is no room to make up for a poor one by adding more. That makes the per-plane production model more important, not less, and it makes a shading survey worth insisting on rather than accepting as a formality.
It also changes how you read a quote. Two proposals for the same roof will differ mainly in equipment and workmanship rather than in scale, so ask what the panels and inverter actually are, what the warranty covers, and who honours it. On a capped system those answers matter more than the headline system size.
Party walls, roof rights and the survey
An attached house meets its neighbour at a party wall, and the roof above it is a boundary question as much as a structural one. Establishing exactly where your roof ends is part of the survey rather than an afterthought, and it is worth having settled before a design is drawn around an assumed area.
Roof form matters too. Where the roof is flat or close to flat, the array is normally mounted on a tilted or ballasted frame, which raises questions a pitched roof does not: what the structure can carry, how the array resists wind, how water still drains, and whether the membrane is penetrated. Those are questions for an on-site assessment rather than an aerial estimate.
Three and four unit buildings hold 9.3 percent of the stock, where roof rights can involve more than one owner and an array feeds a single electrical service, reducing one household's bill rather than splitting between them. Buildings of 20 or more units hold 8.9 percent, where the roof belongs to the owner or the association and a resident cannot commission an installation alone.
Full retail crediting, and the once-a-year settlement
Pennsylvania's Public Utility Commission sets net metering at the full retail rate. Excess generation is credited kWh for kWh against your usage each billing period, so power you export in June offsets power you draw in January at the same rate.
Once a year the utility reconciles any credit still banked at the regulated Price to Compare rate, which is lower than full retail. For a rowhome system that is largely academic: an array capped by roof area is unlikely to generate a permanent surplus beyond a household's own consumption, so most of the credit gets used at full value.
Ask your installer to confirm the current net metering tariff for PPL Electric Utilities specifically. Terms are set per utility rather than statewide, and confirming yours in writing before the design is fixed costs nothing.
Alternative Energy Credits, and what they are actually worth
Under Pennsylvania's Alternative Energy Portfolio Standards Act, the owner of a certified solar photovoltaic system earns one Alternative Energy Credit for every 1,000 kWh generated. Those credits can be sold to electric utilities and suppliers that need them for AEPS compliance, which is a source of value entirely separate from the bill savings.
Getting them requires registering the system and connecting it to the PJM Generation Attribute Tracking System through the Pennsylvania AEPS portal, either directly or through an aggregator or broker. It does not happen automatically when the system is commissioned, and it is worth agreeing with your installer who handles the registration.
The honest qualification is that AEC prices are set by supply and demand on an open market and fluctuate. They are not a reliable income stream. On a smaller rowhome system, which generates fewer credits simply because it generates fewer kilowatt-hours, they are better treated as an occasional extra than as part of the case for the project. Contact an aggregator to confirm current rates before registering, and question any quote that builds a fixed annual AEC figure into its payback.
The 2026 arithmetic
Plan on roughly 1,276 kWh a year for every kW installed. The figure comes from satellite irradiance data with a standard performance ratio applied rather than from measured local systems, so treat it as the number for deciding whether to pursue quotes and let the survey produce the one you contract on.
The 30 percent federal residential tax credit under Section 25D applied through December 31, 2025 and is not available for a purchased home system placed in service after that date. A 2026 purchase in Lancaster cannot claim it, and this is the correction that matters most when reading older material, because a good deal of published solar guidance has not been revised.
If you go solar through a lease or a power purchase agreement instead of buying, the provider may claim the business version of the credit under Section 48E and pass part of that value through in the rate they quote. Ask them directly what they claim and what reaches you, and check it with a tax advisor rather than treating it as an assumption in your own budget.